Activation of electron-emission material



Patented Apr. 10, 1928 UNITED STATES PATENT OFFICE.

JOHN WESLEY MAEDEN, 01 EAST ORANGE, AND JOHN EDWARD CONLEY, OI BLOOI-FIELD, NEW JERSEY, ASSIGNORS T0 WESTINGHOUSE LAIP COMPANY, A CORPORA-TION OI PENNSYLVAN IA.

ACTIVATION OI ELECTBON-EIISSION MATERIAL.

No Drawing.

This invention relates to the activation of material forelectrmi-emission purposes and more particularly to the activation ofsuch material prior to introduction into an electron device.

An object of our invention is the preparation of refractory filamentarymaterial with activating material incorporated therein during the courseof manufacture.

Another object of our invention is the introduction. of carbon intofilamentary material in a more compact form than heretofore, foractivation purposes.

A further object of our invention is the preparation of filamentarymaterial containmg the required amount of electron-emission materialcombined with carbon or mixed with a carbon compound, whereb the volumepercentage of such admixe material may be reduced to facilitate theworking of the filamentar material.

A still furt ier object of our invention is 7 electron-emission materialfor increasing the electron-emissivity thereof.

In the copending application of R. E. Myers, Serial No. 57 8,47 0, filedJuly 29, 1922, activation of thoriated filaments, and assigned to theWestinghouse Lamp Company, there is disclosed a method of preparingthoriated filamentary material with its surface so modified that uponheating, as an electron-emitting cathode, in an electron device, freethorium is developed on the surface thereof.

Briefly, the process comprises passing a thoriated filament, whileheated, through a hydrocarbon atmosphere, comprising such compounds asbenzene vapor or illuminating gas, whereby the thoria in the filament iseither reduced to thorium, changed to thorium carbide or a mixturecomprising one or more of the following materials is formed in or on thefilament :--thorium, thorium carbide and tungsten carbide.

The process described in said application is only applicable foradapting material in Application fled February 81, 1928. Serial No.820,485.

. heating, without further treatment, upon introduction to an electrondevice, carbon and thoria have been mixed with tun ten pow- 'der, whichmixture was subsequent y pressed,

treated and drawn to filamentary form in accordance with usual practice.

The disadvantage in such a procedure lies in the fact that free carbonis relatively light and therefore occupies a relatively large volume inproportion to its weight. The introduction of more than a very smallproportion of carbon in this manner makes 1t more difiicult to work thetungsten to filamentary form, because the difliculty in workingtungsten, where foreign materials are added, is largely dependent uponthe volume percentage of such foreign materials rather than on thepercentage by weight.

To obviate the above noted difliculty, we propose to prepare activatedfilamentary material by mixing with tungsten powder, instead of amixture of thoria and free carbon, either thorium carbide alone, or amixture of thorium carbide and thoria or other thorium compound. Ifthorium carbide is used instead of free carbon, the volume percentage tobe added for introducing the same weight of material is very much lessthan with free carbon. The volume percentage of thorium carbidenecessary would be about A; that of free carbon.

As an'alternative, the mixture of thorium carbide and thoria may beused, in which case, they may be simply mixed with tungsten powder,pressed into a bar or slug,

sintered either by the ordinary method in hydrogen or in a vacuum, ifdesired. Thorium carbide may be conveniently prepared by heating themetal powderto about 900v C. in an atmosphere of illuminating as,benzene vapor or 'other hydrocarbon. or example, thorium carbide wasprepared by heating thorium powder to about 900 C. for from two to threehours in a slow stream of illuminating gas, which was previousl driedbydpassingj through concentrated su phuric ac1 Thorium carbide, alone,may be mixed with tungsten powder, the mixture ressed, treated andworked to the desired lamenamount of carbide b tary form. In thisinstance, there will probably be enough oxide in the tungsten or enoughoxidation introduced during the treatment, to at least partiallydecompose the thorium carbide to cause activation of the material. Onthe other hand, it is not necessary to have any free thorium present oncom leting the working of the wire. If all of 51s thorium is then in theform of thorium carbide, it may be desirable to have it that wa becauseof its greater stability than free t orium.

When heated to a suficiently high temperature after introduction as ahot cathode m an electron device, the thorium carbide will eitherdissociate directly with the liberation of thorium, or will react withoxides present with the liberation of thorium.

In the following detailed description our invention is disclosed forproducing activated tungsten but it is to be understood that we do notwish to be restricted to tungsten for substantially the same method isapplicable for-producin activated molybdenum, tantalum and otier similarrefracto metals.

i f it is desired to use thorium carbide alone for activating thetungsten, the same weight may be used as is ordinarily emp oye'd formanufacturi thoriated tungsten, for example, 1 or 2% or less, by weight,may be admixed with tun car ide and thorium axide or thoria are used, itis only necessary to employ about approximatel half the quantity of thedifferent in ients.

The carbide or carbide and thoria are preferabl very intimately mixedwith tungsten pow er, pressed into slugs of a convenient size, sinteredor heat treated and finally swaged or rolled and drawn to the desiredfilamentary form. The same method of incorporating the carbide orcarbide mixture may be used as is described and claimed in the copendingap lication of W. B. Gero, Serial No. 618,396, led February 10, 1923,manuated that the only change from the customen powder.- If a mixture ofthorium,

ary metho'd of preglaring thoriated filamentary material, who is wellknown to those ski led in the art, is the addition of either thoriumcarbide alone, or admixed with thoria, instead of the usual proportionof c;

thoria.

After drawing to the desired size of wire, the same ma be introducedinto an electron device, as t e hot cathode thereof. Upon heating toincandescence, thorium will be developed or liberated in the filament,either by decomposition of thorium carbide, interaction betweenthoriumcarbide and thorium oxide, or between thorium carbide andtlmgsten oxide. Whatever the precise reaction or combination ofreactions, ood activation is produced because of t ie liberation ordevelopment of free thorium, at least on the surface of the filamentarycathode.

Although thorium has been disclosed as the preferred activatingmaterial, it is to be understood that our invention is applicable foractivating by means of other electronemitters' such as uranium,zirconium and the like.

Although we have described what we now consider the preferred means ofpracticing our invention, it is to be understood that modifications willaccur to those skilled in the art and we on] wish to be restrictedwithin the spirit an scope of the appended claims.

What is claimed is:

1. The method of manufacturing tungsten in filamentary form forelectron-emission purposes comprising mixing with tungsten wder, a smallproportion of thorium caride, pressing said mixture to form a slug,heat-treating said slug and working to the desired filamentary form.

2. Themethod of manufacturing a refractory metal filament for electronemission purposes comprising mixing with the refractor metal powerasmall-pro ortion of a car ide of a metal of good e ectron emissivitagglomerating said mixture into a bar, eat treating said bar and workingand drawing the same to the desired filamentary orm.

In testimony whereof, we have hereunto 1o JOHN WESLEY MARDEN. JOHNEDWARD CONLEY.

